1. Field of the Invention
In assembling micro-optic structures and in particular those utilizing fiber optic waveguides, it is often necessary to control relative spatial alignments with extremely fine precision. Some optical components use optical fibers having a core region that carries a beam of light that is of the order of 10 microns in diameter (and even smaller in some cases). In order to assemble such a component the optical fibers have to be manipulated with a precision level on the order of {fraction (1/10)} of a micron.
2. Prior Art
In the past, optical fibers components have been assembled using known 3-axis ball-bearing positioners. Anyone who has attempted to achieve stable alignment using single-mode optical fiber with such known kinds of positioners equipped with micrometer actuators will attest to the lack of required precision. Crossed roller and ball type stages inherently require preload which generates motional friction and have a resolution limit set by the randomness of the required drive force due to dust and surface variations associated with the frictional interfaces and the limited stiffness of actuator mechanisms.
Other designs of positioners offer frictionless movement with the use of flexure-based designs but often at the expense of overall mechanical stiffness. A single parallel cantilever pair will generate an arc-error in its trajectory. What is commonly done is to combine two cantilever pairs into a compound cantilever stage so as to have one compensate the other and provide perfect linear motion. Compound cantilever stages are very large for their available travel as conventional designs consist of two separate compound stages that are effectively joined at a centerline to maintain high off-axis stiffness. One of the objects of this invention is to provide a compound cantilever stage that is much smaller than the conventional design.
The majority of 3-axis positioning equipment is made up by staging single axis units one on top of each other using angle plates. This results in a structure that has diminished resolution and stiffness as one moves progressively further from the mounting frame of reference. In many designs the stiffness of the overall unit is inadequate to resist the forces required to operate the actuators. In these cases the operator must use a touch and release method where the signal is adjusted and the operator then has to release the actuator to witness the result. Another downfall of a 3-axis positioner made up of three individual orthogonally arranged stages is the fact that the actuators are also arranged in an XYZ configuration, i.e. each has an axis perpendicular to the other two actuators, making prolonged use strenuous due to the required hand movements.
An inherent limitation to the resolution of nearly all positioning systems lies in the use of what can be termed simple axial actuators. A micrometer head or a complex piezo micrometer head are examples of simple actuators as they produce a displacement that is used to control the movement of a translation stage in a direct ratio. For example, a 1 micron movement of the shaft of said actuator is used to produce a 1 micron movement of the corresponding translation stage. As a result, all motional errors such as hysteresis or randomness of movement inherent in the actuator itself are passed on directly to the translation stage. The requirement for sub-micron resolution also necessitates the requirement for differential micrometer and micro-stepped stepper-motor driven lead screw drives in order to achieve the necessary resolution since a single thread micrometer under hand control can""t be easily adjusted at such fine a resolution. The general trend towards increased resolution and stability in positioning equipment has been driven by the increased use of small-core single-mode optical fibers over the larger core multimode optical fibers which require less precision in alignment manipulation. In order to remove the effect of operator induced forces, a number of sub-micron resolution remote driven motor driven stages have emerged on the market. Even with fully automated positioning systems where a scan routine is carried out under computer control, some level of operator intervention is required for handling and loading the individual elements to be assembled. In many labor intensive assembly applications the cost of an automated system cannot be justified and would not be considered if an appropriate mechanical positioner were available.
It is the object of this invention to realize a 3-axis positioning device ideally suited for, but not limited to, the assembly of single-mode fiber optic components. The invention allows for all of the actuators to be placed in a common orientation to reduce hand fatigue and improve adjustment efficiency. The invention teaches a structure that provides for both coarse and fine movement while using a simple adjustment screw and a single actuator such as a micrometer head or a motorized stepping or DC motor driven actuator. The structure also allows for the fine movement to be a fraction of the travel of the control actuator while increasing movement resolution. Another aspect of the invention includes means of translating motion from one axis of movement to another. In addition, the invention teaches a linear compound flexure stage that provides for large travel and linear motion with high stiffness. In its preferred form, the invention can provide for operator insensitive adjustment when aligning single-mode optical fibers with a resolution limit that is comparable to a closed-loop piezo driven translation stage.
The invention is an improvement over a conventional stacked 3-axis unit as the operator adjustment forces act only on a single stiff linear translation stage instead of the sum of the total of all stages. It is thus possible to realize a positioning device that can operate under hand control at resolution and stiffness levels required for single-mode fiber optic alignments wherein the operator does not influence the measured optical signal level during adjustment of the unit. It is also possible with the invention to implement linear motor drive on the second and third axes without affecting the overall sensitivity to hand adjustment forces.
According to one aspect of the invention, a positioning device includes:
a first, normally fixed support;
a movable support mounted on said fixed support and constrained to move in a generally rectilinear manner in a first direction;
a first actuator mounted on the fixed support for moving the movable support in the first direction;
a second actuator mounted on said movable support in substantially parallel relationship to the first actuator;
holding means for an object to be positioned, the holding means mounted on said movable support for movement relative to said movable support in a second direction which is perpendicular to said first direction; and
an orthogonal drive conversion system for converting motion of said second actuator in the first direction to movement of the holding means in the second direction.
The orthogonal drive conversion system serves to isolate the holding means from manual forces applied to the second actuator.
The orthogonal drive conversion system may include an actuator mechanism having a push rod pivoted at a first of its ends to means movable by the second actuator, and at a second end, to motion translation means for converting motion of the push rod to movement of the holding means in the second direction.
Preferably, the device includes both second and third actuators mounted on the movable support in parallel relationship to said first actuator; and the holding means is mounted on the movable support for movement relative to the movable support in second and third directions which are perpendicular to the first direction and perpendicular to each other. First and second orthogonal drive conversion systems are provided for converting motion of said second and third actuators respectively to movement of the holding means in said second and third directions. Each orthogonal drive conversion system may include an actuator mechanism including a push rod pivoted at a first end to means movable by the respective second and third actuators, and at its second end to motion translation means for converting movement of the push rod to movement of the holding means in the respective second and third directions.
One aspect of the invention is a compound cantilever stage that is one-half of the conventional design, the latter using two separate compound stages that are effectively joined at a centerline to maintain high off-axis stiffness. Traditionally, the one-half arrangement is not used as the intermediate frame of reference would move in response to external loads placed on the system and limit off-axis stiffness. It can be shown however, that if the intermediate frame in a compound cantilever stage were to be forced to move one-half of the overall displacement, then high stiffness can be achieved while requiring only one half of the conventional compound cantilever design. An aspect of this invention is to provide a forcing or control means to set the displacement of the intermediate frame of reference of a compound cantilever stage to one half of the output displacement. In its preferred form, the control means is a beam member connected to the parts by frictionless elastic elements.
In accordance with this aspect of the invention, a positioning device includes:
a first, normally fixed support;
a movable support movable in a generally rectilinear manner in a first direction and carrying holding means for an object to be positioned;
an intermediate member which is connected to said first support by a pair of first spaced flexible elements and which is connected to the movable support by a pair of second spaced flexible elements; the arrangement being such that the first flexible elements and the second flexible elements are approximately of the same length: and control means connecting said fixed support, said intermediate member and the movable support so that the movement of the intermediate member is a fixed proportion of the movement of the movable support.
Preferably, the control means comprises a rigid member connected to the intermediate member at a position midway between its connections to the fixed support and the movable support, so as to ensure that the movement of the intermediate member is about one-half that of the movable support.
Another aspect of the invention provides a lever type mechanical advantage between the actuators and the mechanism producing movement in the second and third directions. In accordance with this aspect, the positioning device includes:
a support;
holding means for an object to be positioned, the holding means mounted on said support for movement in a particular direction;
an actuator mounted on said support, and
an orthogonal drive conversion system for converting motion of the actuator to movement of the holding means in said particular direction, said conversion system including an actuator mechanism and a motion translation means;
said actuator mechanism including a lever having a first end connector point movably connected to the actuator, the lever having a second end portion which has second and third spaced connector points which form a triangle with the first end connector point, the second spaced connector point being located by a contact element and the third spaced connector point being located by an adjustment screw providing an adjustment which is coarse relative to the actuator, and wherein said lever has a fourth connector point in contact with a push rod which transmits motion of the lever member to the motion translation means.
The fourth connector point is positioned so that the movement of the push rod is a fraction of the movement of the actuator.
Yet another aspect of the invention relates to the nature of the motion translating means which connect the push rod or like means to the holding means. In accordance with this aspect of the invention, the positioning device includes:
a fixed support;
a movable support movable in a generally rectilinear manner in a first direction and carrying holding means for positioning an object, and also carrying an actuator,
an orthogonal drive positioning conversion system for converting motion of said micrometer type actuator to movement of the holding means in a particular direction which is perpendicular to the axis of the actuator, said conversion system including an actuator mechanism and a motion translation means, said actuator mechanism including a push rod movable by the actuator; and
an angularly movable part which is connected to an element fixed to said movable support by two crossing flexible elements which preferably extend perpendicularly to each other, said angularly movable part being also connected to said holding means in such manner that when angularly moved by said push rod the angularly movable element produces movement of said holding means in said particular direction which is perpendicular to the first direction.
Preferably, the crossing flexible elements, when viewed along the axis of rotation of the angularly movable part, cross each other between the fixed element and the angularly movable part at the approximate centers of the crossing flexible elements.